Starches occur in nature in the form of discrete granules. When a suspension of granular starch is heated in water to a point above its gelatinization temperature, the granules undergo hydration and gelatinize to form a viscous dispersion or paste. This property has led to the use of starch as a thickening agent, particularly in food applications.
It is well known that if one simply adds starch, or a mixture containing starch, to boiling water, the starch rapidly forms lumps which cannot be dispersed even with the most vigorous and extended stirring. The lumps are formed when clusters of starch granules contact the hot water. The outer portions of the starch clusters immediately gelatinize, and this "coating" of gelatinized starch forms a barrier against water penetration into the clusters.
One way to overcome the lumping problem is to disperse the starch completely in cold water before the mixture is heated and gelatinized. This method is time consuming and for many applications it is necessary, or preferable, to add the thickening agent to the hot liquid.
Starches can be made more readily dispersible in hot water by complexing them with a surfactant. This method involves mixing native starch, water and a surfactant at a suitable temperature for a sufficient time to impart the desired properties to the starch without causing substantial gelatinization of the starch granules. While this method has proven to be satisfactory for modifying starches of roots and tubers, such as tapioca and potato, it is less satisfactory when applied to corn starch. If such a corn starch-surfactant complex is stirred in boiling water, the paste tends to be lumpy even though it develops a fairly high viscosity.
Starches have also been treated with UHF (ultra-high frequency) radiation, also known as microwave radiation, in order to modify their properties. This method gives starches which are somewhat more dispersible in hot water than native starch. However, these starches are either not completely dispersible in hot water or their dispersions do not give the viscosity required for a thickening agent.
A process has now been discovered that gives a modified corn starch which is substantially completely dispersible in hot water. Furthermore, its hot-water dispersion has a high viscosity making it suitable for use as a thickening agent in food and other applications.